Infantile-onset Pompe disease (GSD-II; MIM 232300) is a lysosomal storage disease associated with muscle weakness, hypotonia and lethal cardiomyopathy during infancy, whereas late-onset Pompe disease features progressive weakness without significant cardiomyopathy (Kishnani et al, J. Pediatr. 148:671-676 (2006), Hirschhorn et al, The Metabolic and Molecular Basis for Inherited Disease, Scriver et al (eds.), McGraw-Hill, New York, pp. 3389-3419 (2001)). The histopathology of Pompe disease includes progressive lysosomal accumulation of glycogen in cardiac and skeletal muscle. The in vivo efficacy of enzyme replacement therapy (ERT) for Pompe disease was first demonstrated in the GAA-deficient Japanese quail by both clinical and metabolic correction (Kikuchi et al, J. Clin. Invest. 101:827-833 (1998)), and then later in the GAA-knockout (GAA-KO) mouse model by reducing glycogen accumulation and restoring GAA activity in the heart and skeletal muscle (Bijvoet et al, Hum. Mol. Genet. 8:2145-2153 (1999), Raben et al, Mol. Genet. Metab. 80:159-169 (2003)). The preclinical data justified an initial Phase I/II clinical trial (Kikuchi et al, J. Clin. Invest. 101:827-833 (1998), Amalfitano et al, Genet. Med. 3:132-138 (2001)). Further development of recombinant human (rh)GAA involved two pivotal clinical trials differing primarily by age upon entry. Study 1 enrolled subjects less than 6 months old and demonstrated prolonged survival in response to rhGAA therapy; furthermore, all 18 patients were alive at age 18 months and 15/18 (83%) showed invasive ventilator-free survival at age 18 months (Kishnani et al, Neurology 68:99-109 (2007)). Study 2 enrolled subjects 6-36 months old and demonstrated improved survival, although no difference in ventilator dependence was realized. Both protocols improved cardiomyopathy, growth and motor development; however, the more robust outcomes in study 1 emphasized the value of early treatment in infantile Pompe disease.
The main limitation of ERT in Pompe disease is a well-recognized variability of response by skeletal muscle. Potential factors involved in this variability include extent of muscle damage at the start of ERT, a lower number of mannose-6-phosphate receptors in skeletal muscle in comparison to the heart; resistance to correction by type II myofibers; and the formation of high titer antibodies in the cross-reacting immunologic material (CRIM) negative patients (Kishnani et al, Neurology 68:99-109 (2007), Raben et al, Mol. Ther. 11:48-56 (2005), Kishnani et al, J. Pediatr. 149:89-97 (2006)).
Animal and human studies have suggested that antibody formation to rhGAA reduced the efficacy of ERT. For instance, GAA-KO mice produced anti-GAA antibodies in response to intravenous rhGAA, and died following subsequent injections (Raben et al, Mol. Genet. Metab. 80:159-169 (2003)). In the first pilot study of ERT using CHO cell-derived recombinant hGAA, both CRIM-negative Pompe disease subjects had markedly reduced efficacy from ERT in association with high titer antibodies against hGAA (Amalfitano et al, Genet. Med. 3:132-138 (2001)). Phase II and III studies revealed that patients with the highest, sustained titers of antibody had the least favorable outcome (Kishnani et al, Neurology 68:99-109 (2007), Kishnani et al, J. Pediatr. 149:89-97 (2006)) The similarity with regard to the antibody response in GAA-KO mice and in CRIM-negative Pompe disease patients could be linked to the lack of residual GAA protein expression.
Intravenous administration of adenovirus vectors encoding GAA transiently corrected the glycogen storage in the striated muscle of GAA-KO mice (Amalfitano et al, Proc. Natl. Acad. Sci. USA 96:8861-8866 (1999), Pauly et al, Hum. Gene Ther. 12:527-538 (2001)), although glycogen gradually re-accumulated coincident with the formation of anti-GAA antibodies (Ding et al, Hum. Gene. Ther. 12:955-965 (2001)). Even when GAA-KO mice were tolerized to hGAA by neonatal administration of the recombinant enzyme, only a subset of those mice failed to produce anti-GAA antibodies in response to administration of an adeno-associated virus (AAV) vector containing a viral promoter to drive human (h)GAA expression (Cresawn et al, Hum. Gene Ther. 16:68-80 (2005)). In marked contrast, administration of AAV vector containing a liver-specific promoter evaded immune responses to introduced hGAA in response to only 1010 vector particles, and achieved near-total clearance of accumulated glycogen from skeletal muscle with a 10-fold higher vector quantity (Franco et al, Mol. Ther. 12:876-884 (2005), Sun et al, Mol. Ther. 14:822-830 (2006)).
Liver-specific expression has accomplished immune tolerance to therapeutic proteins in several genetic disease models resulting from a null mutation, including mice with Pompe disease. Immune tolerance was established through high-level liver-specific expression, as demonstrated through dose-reduction experiments in hemophilia B (MIM 306900) mice (Mingozzi et al, J. Clin. Invest. 111:1347-1356 (2003)). Furthermore, the use of a muscle-specific promoter failed to prevent antibody responses to the therapeutic protein in either hemophilia B or Pompe mice (Liu et al, Hum. Gene Ther. 15:783-792 (2004), Sun et al, Mol. Ther. 11:889-898 (2005)). A unique liver-specific promoter derived from the thyroid hormone-binding globulin promoter sequence (denoted as the LSP) prevented the antibody response against factor IX and against GAA in immunocompetent mice (Franco et al, Mol. Ther. 12:876-884 (2005), Wang et al, Proc. Natl. Acad. Sci. USA 96:3906-3910 (1999)), and its activity was highly restricted to the liver as compared to muscle (Franco et al, Mol. Ther. 12:876-884 (2005)). The relevance of liver-specific expression to therapy in lysosomal storage disorders was further emphasized by the ability of a different liver-specific promoter to prevent the formation of antibodies against α-galactosidase in Fabry disease (MIM 301500) mice (Ziegler et al, Mol. Ther. 9:231-240 (2004), Ziegler et al, Mol. Ther. 15:492-500 (2007)). The mechanism for achieving immune tolerance, although incompletely understood, clearly depends upon the induction of regulatory T cells that repress the formation of cytotoxic T cells (Mingozzi et al, J. Clin. Invest. 111:1347-1356 (2003), Ziegler et al, Mol. Ther. 15:492-500 (2007), Hoffman et al, Hum. Gene. Ther. 18:603-613 (2007)). The LSP reduced the γ-interferon response to introduced GAA expression in comparison to a universally active promoter, consistent with abrogation of the cytotoxic T cell responses (Franco et al, Mol. Ther. 12:876-884 (2005)).
The present invention results, at least in part, from studies designed to test the hypothesis that AAV-vector mediated gene therapy can induce tolerance to introduced GAA. The results demonstrate that this strategy can enhance the efficacy of ERT in CRIM-negative Pompe disease patients and in patients suffering from other lysosomal storage diseases. This strategy can also be used to enhance the efficacy of coagulation therapy in patients suffering from hemophilia.